1. Field of the Invention
The present invention relates to a shutter blade apparatus including a shutter blade that blocks and unblocks an opening, a shutter unit, an image pickup apparatus, an exposure apparatus, and a method of manufacturing a device using the exposure apparatus.
2. Description of the Related Art
In general, reduction projection exposure apparatuses and the like have been used for manufacturing semiconductor devices and the like. The reduction projection exposure apparatuses reduce the size of patterns formed on originals, such as reticles, using reduction projection lenses and project the reduced patterns onto substrates such as wafers. The pattern of a reticle is transferred to several tens of positions on a wafer by alternately repeating step driving of an XY stage and exposure. Recently, in order to improve the productivity of the exposure apparatuses, efforts have been made to reduce the cycle time during exposure by increasing the opening and closing speed or the like of shutters disposed on paths of exposure light. Moreover, in order to reduce the time required for exposure, the sensitivity of a resist applied to wafers or the like has been rapidly improved.
According to the above-described known technology, a shutter blade constituting a shutter in a light-source optical system that generates an exposure light beam is inserted into a path of the exposure light beam so as to block the light beam. Thus, the size of the shutter blade needs to be larger than the cross-section of the exposure light beam. Moreover, when the shutter is closed, the shutter blade absorbs the heat of the exposure light beam, and can be deformed or melted. Accordingly, the surface of the shutter blade in general has a mirror-like finish so as to reflect the exposure light beam. In addition, when the exposure light beam reflected by the shutter blade travels back to the light source, thermal fluctuations can be generated in the light source. Therefore, the shutter blade in general is obliquely inserted into the path of the exposure light beam such that the light beam reflected by the shutter blade does not travel back to the light source. With this arrangement, the cross-section of the light beam blocked by the shutter blade becomes elliptical.
Therefore, the size of the shutter blade needs to be still larger than the cross-section of the light beam perpendicular to the light path when only one shutter blade is used for blocking the light beam. On the other hand, the opening and closing speed of the shutter needs to be increased in order to improve the throughput of the exposure apparatus. Accordingly, the weight of the shutter blade needs to be reduced while the required cross-section of the shutter blade is maintained. To this end, the thickness of the shutter blade may be reduced by using a light and heat-resistant metallic material for the shutter blade. Some known technologies intend to reduce the weight of the shutter blade while the cross-section required for blocking the exposure light beam is maintained. Japanese Patent Laid-Open No. 11-233423, for example, describes a shutter for exposure facilitating an increase in the opening and closing speed.
The known technology will now be described with reference to FIGS. 7A and 7B. A shutter 40 formed of a pair of rotary shutter units 40a and 40b is disposed on a path of an exposure light beam 100 to which a wafer or the like is exposed. The rotary shutter units 40a and 40b are synchronously rotated by motors 45a and 45b, respectively. As shown in FIG. 7B, for example, the exposure light beam 100 is blocked or unblocked by the rotation of shutter blades 41a to 43a and shutter blades 41b to 43b of the rotary shutter units 40a and 40b, respectively. That is, the rotary shutter unit 40a partially blocks the upper half or more of the exposure light beam 100 in a successive manner using the three shutter blades 41a to 43a that are obliquely inserted into the path of the exposure light beam 100. Similarly, the rotary shutter unit 40b partially blocks the lower half or more of the exposure light beam 100 in a successive manner using the three shutter blades 41b to 43b that are obliquely inserted into the path of the exposure light beam 100.
The three shutter blades 41a to 43a and the three shutter blades 41b to 43b of the rotary shutter units 40a and 40b, respectively, form light-shielding portions each having a central angle of 60° disposed at intervals of 60° in a circumferential direction of rotating shafts 44a and 44b, respectively. The shutter blades 41a to 43a and the shutter blades 41b to 43b of the rotary shutter units 40a and 40b, respectively, are rotated in connection with the rotation of the rotating shafts 44a and 44b driven by the motors 45a and 45b, respectively. The rotating positions of the shutter blades are detected by rotary encoders 46a and 46b. In the above-described known technology, the size of the shutter blades can be reduced as compared with the case where only one shutter blade is used for blocking the entire exposure light beam 100. Accordingly, the moment of inertia of the shutter blades can be reduced, thereby facilitating an increase in the opening and closing speed of the shutter.
However, in the known technology described in Japanese Patent Laid-Open No. 11-233423, the rotary shutter units 40a and 40b need to be synchronously rotated using the motors 45a and 45b, and a difference in velocity of approximately sub-milliseconds is generated by factors such as mechanical structures. Furthermore, in order to equalize the distribution of the amount of exposure light applied in the exposure area of the wafer, both edges of the shutter blades 41a to 43a and the shutter blades 41b to 43b shown in FIG. 7B crossing the exposure light beam 100 need to have the same shape. Thus, the difference in velocity between the shutter blades 41a to 43a and the shutter blades 41b to 43b can exert detrimental effects on the distribution of the amount of exposure light in the above-described known technology.
On the other hand, only one shutter blade is used for blocking an exposure light beam while the thickness of the shutter blade is reduced such that the weight of the shutter blade is reduced in some technologies. However, the amount of light when the shutter is closed needs to be smaller than or equal to one-millionth of that when the shutter is fully opened. Therefore, in order to improve the blocking performance of the shutter, a shielding plate needs to be disposed in the vicinity of an opening that is to be blocked or unblocked by the shutter blade so as to be adjacent to the shutter blade. At this moment, when the stiffness of the shutter blade is reduced due to the low-profiled shutter blade, the shutter blade can be deformed by the weight thereof or a centrifugal force or the like during the rotation thereof, and can come into contact with the shielding plate. This can prevent normal operation of the shutter.